Technical Field
Embodiments of the invention relate generally to power electronics. Particular embodiments relate to apparatus and methods for filtering the voltage output from gradient power amplifiers that are used in magnetic resonance imaging (MRI) systems.
Discussion of Art
Generally, the quality of images produced by an MRI system will be affected by the repeatability and fidelity of its electronic components. In particular, gradient subsystem power amplifiers strongly influence the fidelity with which a scan volume is voxellated (scanned in volume segments of equal size and common orientation). Power amplifier ripple or oscillation can degrade a desired uniformity of voxel size and orientation.
Accordingly, MRI systems are provided with apparatus for correcting images in response to deviations in the performance of electronic components such as the gradient subsystem power amplifiers. One such apparatus is a ripple cancellation filter, which is provided to reduce switching noise produced at the gradient coil caused by pulse width modulating the gradient power supply. Typically, ripple cancellation filters are designed to cancel noise around a single fundamental frequency that is driven by a pulse width modulation (PWM) switching frequency of the MRI system in which the filters are installed. In case an MRI system might be operated at any of plural PWM switching frequencies, then plural ripple cancellation filters are installed.
In view of the above, it is desirable to provide apparatus and methods for efficiently implementing a multi-notch ripple cancellation filter that is usable in MRI systems capable of operating at plural PWM switching frequencies. Such apparatus and methods might also be helpful toward filtering the outputs of PWM power supplies, generally.